Add 'unsafeEncodeUtf' from os-string #227

Job	Run time
i386	4m 36s
arm (arm32v7)	10m 58s
darwin_arm (self-hosted, macOS, ARM64, 8.10.7)	55s
arm (arm64v8)	3m 51s
build (ubuntu-latest, 8.6, 3.8.1.0)	5m 28s
darwin_arm (self-hosted, macOS, ARM64, 9.2.6)	47s
build (ubuntu-latest, 8.8, 3.8.1.0)	5m 32s
darwin_arm (self-hosted, macOS, ARM64, 9.4.4)	49s
build (ubuntu-latest, 8.10, 3.8.1.0)	5m 49s
build (ubuntu-latest, 9.0, 3.8.1.0)	5m 18s
build (ubuntu-latest, 9.2, 3.8.1.0)	4m 4s
build (ubuntu-latest, 9.4, 3.8.1.0)	4m 24s
build (ubuntu-latest, 9.6, 3.8.1.0)	2m 57s
build (ubuntu-latest, 9.8, 3.8.1.0)	3m 24s
build (macOS-latest, 9.4, 3.8.1.0)	1h 34m 1s
build (macOS-latest, 9.6, 3.8.1.0)	15m 29s
build (windows-latest, 9.4, 3.8.1.0)	3m 11s
build (windows-latest, 9.6, 3.8.1.0)	3m 0s
	2h 54m 33s

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